The present invention relates to a magenta ink composition (this term includes both a dark magenta ink composition and a light magenta ink composition) suitable for ink jet recording.
In recent years, an ink jet recording method has attracted attention. The ink jet recording method is a printing method in which printing is carried out by making small drops of an ink composition fly onto and thus become attached to a recording medium such as paper. This method has the distinctive characteristic that high-quality high-resolution images can be printed at high speed using a relatively inexpensive apparatus. Ink jet recording apparatuses using this method have found wide commercial acceptance due to good print quality, low cost, relatively quiet operation, and ability to form graphics. Among ink jet recording apparatuses, thermal (bubble jet (registered trademark)) and piezoelectric drop-on-demand printers have been especially successful on the market, and have come to be widely used as printers for personal computers in offices and households.
These days, formation of color images is carried out by preparing a plurality of color ink compositions and carrying out ink jet recording. In general, color images are formed using ink compositions of three colors, i.e. a yellow ink composition, a magenta ink composition and a cyan ink composition, or in some cases four colors, with a black ink composition added. Furthermore, color images may also be formed using ink compositions of six colors, with a light cyan ink composition and a light magenta ink composition added to the above four colors, or seven colors, with a dark yellow ink composition further added. The ink compositions used in such formation of color images are each required to have good colorability themselves, and in addition when a plurality of the ink compositions are combined, it is required to able to produce good intermediate colors, printed articles are required not to discolor or fade during subsequent storage, and so on.
Moreover, in recent years, through continual improvements in all of heads, ink compositions, recording methods and media, ‘photographic image quality’ printing using color ink jet printers has reached a level that stands comparison with ‘silver salt photography’, and the image quality has reached ‘photograph-equivalent’. On the other hand, with regard to the storability of obtained images, attempts have been made to improve the characteristics through improving ink compositions and media. In particular, with regard to light-fastness, the characteristics have been improved to a level at which there is no longer a problem in terms of practical use (see Japanese Patent Application Laid-open No. 2000-290559, Japanese Patent Application Laid-open No. 2001-288392). However, things are still not on a par with silver salt photography. When evaluating light-fastness, it is standard for judgement to be carried out using as an index the fading rate for pure color patterns (optical density around 1.0) for each of yellow, magenta and cyan. Upon judging the light-fastnesses of ink compositions loaded into printers currently sold on the market using this evaluation method, it is often the case that the light-fastness is lowest for the magenta ink composition, and hence the magenta ink composition determines the light-fast lifetime for the ink set as a whole. Improving the light-fastness of the magenta ink composition would thus lead to an improvement in the light-fastness of photographic images and a lengthening of the light-fast lifetime for the ink set as a whole.
Moreover, printed articles produced using ink compositions as described above are placed of course indoors and also sometimes outdoors, and hence are exposed to sunlight and various other types of light and also the outside air (ozone, nitrogen oxides, sulfur oxides, etc.); ink compositions having excellent light-fastness and gas resistance are thus being developed. The characteristics of light-fastness and gas resistance are greatly influenced by the colorants in the inks, and hence there are calls for the development of magenta ink compositions that are excellent in terms of these characteristics, and also moisture resistance.
As colorants having excellent light-fastness and gas resistance out of the above characteristics, compounds (azo dyes) described in Japanese Patent Application Laid-open No. 2002-371079, and compounds (anthrapyridone dyes) described in Japanese Patent Application Laid-open No. 2002-332419 have been proposed.
Moreover, with an ink set containing a light magenta ink as described above, by including two magenta ink compositions of different color densities, it has become possible to obtain images with no graininess. With regard to such ink sets containing two ink compositions having different color densities in this way, which are principally for printing photographic images, in general it is often the case that the ink composition having a low color density is used to alleviate/eliminate graininess when forming photographic images. Moreover, when evaluating the light-fastness as described above, a pattern having an optical density of around 1.0 is formed with the ink composition having a low color density. Improving the light-fastness of the light magenta ink composition thus again leads to an improvement in the light-fastness of photographic images and a lengthening of the light-fast lifetime for the ink set as a whole. With an ink composition having a low color density, compared with an ink composition having a high color density, not such high colorability is required, and hence other characteristics such as the light-fastness become important.